


Heat of the Moment

by Nightlydemon



Category: Underfell - Fandom, Undertale (Video Game)
Genre: M/M, Mating Cycles/In Heat
Language: English
Status: Completed
Published: 2019-07-29
Updated: 2019-07-29
Packaged: 2020-07-25 20:23:30
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 1,999
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20031805
Author URL: https://archiveofourown.org/users/Nightlydemon/pseuds/Nightlydemon
Summary: Sans sticks around after hours to help Grillby with something.You all know it's blatant Underfell Sin, nothing else really needs to be said about it.





	Heat of the Moment

Sans tapped his finger on the bar waiting for his burger and fries. It'd been a bit longer of a wait than he was used to, but there was no way he was going to eat with his brother. He couldn't stand hearing an endless lecture about how much he slacked off on his sentry duties. Why did Papyrus have to be so uptight about that? It's not like anything ever happened that far out in the woods. He stretched his arms over his head and popped his cervical vertebrae to ease the building tension. A few nasty jeers were directed at him from the other patrons, but he ignored them. Random comments from cowards were still better than a predictable tongue lashing from his little brother. Grillby emerged from the kitchen and set a perfectly cooked and plated burger with a side of fries. The little skeleton cocked an eyebrow at the curious sight. His burgers were usually a little over cooked. A few seconds later a glass of the fire monster's best wine was set beside the plate.

“Grillbs, I didn't order that,” Sans commented.

“It's on the house. I need you to stay after hours to help me with something. I'm bribing you with good wine,” Grillby responded. His fire was looking a little more blue than purple as he went back to serving the other patrons.

Sans shrugged and picked up the closest bottle of mustard. Before he could drizzle some over his fries, the tall fire monster pulled the bottle away and replaced it with a different bottle. The little skeleton blinked before coating his fries. The mustard was a little more brown than normal with little bits of black stuff, but it was whatever. He popped a mustard covered fry in his mouth and the rest of the bar faded into nothing.

The flavors danced with perfect rhythm across Sans tongue. The mustard flavor was perfectly set off by the earthiness of black truffle. He took a bite of the beautiful burger and tears formed in the corners of his sockets. The delicious combination of expertly sauteed stoic onions, caciotta cheese, and dried Waterfall kelp really set off exquisitely grilled burger. The bun was buttered and toasted with extreme care. The little skeleton took a sip of wine and the pairing was perfect. The entire meal was just too delicious to scarf down like normal. He savored every little bite and let the joy wash through his entire being.

Almost an entire hour passed before Sans finished the last bite. He still had half the wine left as he looked towards his fiery friend. Grillby was looking a little more blue and looked like he was starting to get irritated about the bar still being open. The light fuzz of slightly tipsy started to tickle the little monster's mind as he slowly sipped his wine. He finished and moved on to sipping the black truffle mustard as last call was announced.

Sans lightly nibbled on the spout of the mustard bottle as he started to wonder what Grillby could need him to help with. It wasn't the first time that hothead had asked him to do something after hours, but it was definitely the first time he'd been bribed with such an elaborate meal. It had to be a bigger deal than the standard past curfew contraband delivery or pick up. It didn't take long for the impatient, now totally blue, fire monster to shoo all the other patrons out of the bar. The little skeleton swiveled around at the sound of the front door locking.

“So, whatcha need? It can't be the usual. Ya got a heist planned or somethin'?” Sans asked as he watched the blinds over the bay window lower. Grillby turned towards the bar and walked slowly towards the skeleton. He shed his fur collared coat and abandoned it on a nearby table as he worked the buttons on his shirt open. It was fully open to reveal a finely toned chest of flickering blue flame by time the taller monster reached the bar. The skeleton pulled himself closer to the bar, worried sweat dripping down his skull.

“Sans. I need you,” Grillby stated. He leaned over the little monster until his face was within inches. The skeleton opened his mouth to say something. “I'm in Heat, Sans. I need _you_.”

“I got some spare suppressants right here,” Sans said as he relaxed and pulled the little pill bottle from his jacket. The bottle was smacked across the bar before a flaming hand pulled the skeleton into a passionate kiss. Grillby's other hand found it's way up the little monster's shirt and curled gently around his ribs. He let out a muffled moaned at the sensation of being touched. The kiss broke as both monsters breathed heavily.

“My last dose wore off five hours ago,” Grillby commented.

“Damn, Grillbs! Yer gonna explode at this rate,” Sans blurted. “I guess I'll help ya. Yer self-control is kinda scary, by the way.”

Grillby hoisted the little skeleton onto the bar and buried his face in his neck. His flaming tongue lapped at Sans neck. The skeleton gasped as his friend's natural heat penetrated his bones before shrugging off his hoodie. The fire monster pushed his hand into the small monster's shorts and gently caressed his pelvis. The little monster felt his ecto start to form and his dick twitched to life in the blue flame hand. The fire monster let out an aggressive growl.

“Change it!” Grillby demanded. Sans swallowed hard as he fell further into a submissive head space. He focused on the shape of his magic until his cock morphed into a dripping pussy. Two flaming fingers plunged into the glowing red magic. The little skeleton gasped and held onto the fire monster tight as the new sensation. A flickering thumb pressed into his virgin nub and moved in slow circles. The raw pleasure had him whimpering with want at the sound of the taller monster's pants hitting the floor. A hot hand pushed the little monster's sweater up and traced the curve of his ribs.

Grillby trailed his tongue down the exposed sternum in front of him. He pulled Sans shorts off and he allowed a primal purr to rumble form his throat. He placed a gentle nip to the little skeleton's hip and quickly engulfed the glowing nub with his mouth. He moved his fingers as if to beckon fourth his friend's desire. His tongue flicked at the firm button to tease delicious sounds from the little monster in his clutches. Skeletal fingers buried into the hot flames of the taller monster's hair. He almost lost control over his magic with the unrelenting waves of pleasure, but the little skeleton managed to keep the shape. The song of pleasure echoed off the walls of the empty bar.

Sans was right at the edge when Grillby stopped licking his ecto-pussy. He looked down at his best friend with half closed sockets and mild confusion. The fire monster had started to shift back to purple, most of the blue now focused in his torso. The little skeleton followed the flow of color to very bright, very massive fire cock. His sockets opened wide as his body tensed.

“Uh, Grillby. I'm not sure that's gonna fit,” Sans commented. The fire monster stood slowly and let his hands trail up the little monster's bones. His fiery tongue dove into his friend's mouth. The little monster was pulled forward to grind into the white hot cock. The flickering head started to press into his folds and the little monster tried to pull away.

“Hold still, it'll fit,” Grillby growled. He pushed slowly into Sans magic and stretched it wide. The little skeleton gripped into the fire monster's firm back and bit into his shoulder. It wasn't really pain, but more an uncomfortable intrusion. The larger monster made careful thrusts, reaching deeper with each one. The little skeleton released his friend's shoulder to cry out when he hilted.

“Grillbs! D-don't move yet! P-please!” Sans managed to get out. Grillby's dick curled and twitched constantly like it had a mind of it's own. The fire monster pulled the little skeleton into a deep, passionate kiss before he started to grind into the other's slick magic. It didn't take long before he made full thrusts into his prey. The two monsters mewled out their ecstasy. Soon they were just a flurry of tangled bliss.

“G-grillby! F-fuck, I-I'm gonna cu-shit, gonna cum,” Sans called out. The fire monster took it as a sign to rut harder.

“D-don't, hah, you dare!” Grillby hissed. “I-if you do, gah, I'm n-not g-gonna stop!”

Sans ran his fingers down the larger monster's back trying to hold out a little longer. The skeleton gripped tighter into the fire being slamming into him as a tight coil threatened to unleash. He fought back as hard as he could, but the urge won. The little skeleton felt his magic clench down and his ecto splattered to the floor. Grillby let out a groan as he continued to thrust hard into his friend's twitching ecto-pussy.

“G-Grillby! I-it's too much,” Sans groaned out. The fire monster slammed his little body into the bar and gripped his wrists hard. The blue of his fire was more centered as his pace became more brutal. The skeleton tried to focus more on keeping his magic in the right shape as his mind melted into sub-space. Tears trickled down his skull from the over stimulation.

“I t-told you! Now take, hng, take it!” Grillby demanded. The fire monster leaned down and bit into Sans clavicle. The little skeleton let out a sharp yelp of pleasure. The fire monster slammed into him over and over again. This was his life now. It could be worse. The tightness began to rebuild the longer the now mostly purple fire monster rutted hard. Soon the fire monster started to falter in his rhythm and the little skeleton tried to fight against his looming second release.

“Grillbs!” Sans cried out as he felt his magic clench down again. A few thrusts and he was still in the midst of ecstasy release. Grillby let go of the little monster's clavicle and groaned out his pleasure. His flickering cock started to twitch in anticipation.

“S-Sans!” Grillby moaned out as his release took over. The little skeleton's pulsing ecto had tipped him over the edge as he spilled all of his heat into the monster. The hot, blue goo dripped to the floor as the fire monster began to fully shift back to purple. The two monsters panted in each other's arms. When the larger one pulled away, the little skeleton collapsed to the floor, completely spent. The fire monster stumbled to the bottle of pills that got tossed across the bar and swallowed a couple.

“S-so, that happened,” Sans mused. He pulled himself up to his feet and started to pull his clothes back on. He stumbled a little as he reached for his hoodie.

“Y-yeah... About your tab... Keep this between us, and it's gone,” Grillby said. He was in the process of putting his clothes back on. The fire monster summoned his soul and examined it. He let out a sigh of relief before putting it back in his flames. Sans paused for a second.

“So, I read in one of my brother's books that after,” the little skeleton hesitated trying to find the right words. “Well, after the first time that affection is supposed to... grow. Are you... And me-.”

“No,” Grillby snapped.

“Oh, good cuz I don't really wanna wake up ta yer mug every mornin',” Sans commented with a sigh of relief. The fire monster spun around with an expression of insult about to say something. “See ya tomorrow!” The little skeleton plipped out of the bar and into his room. He landed softly on his bed and quickly fell asleep.


End file.
